Human/machine interfaces for electronic machines commonly include key assemblies or arrays thereof that convert a human operator's mechanical input into an electrical output. The key assembly arrays are typically part of keyboards for computers and part of keypads for telephones, calculators, and mobile game devices. The key assembly arrays may also be used in television and/or entertainment center remote control transmitters. Many other electronic machines also use such key assemblies.
Iwasaki (Japanese Laid-Open (Kokai) Patent Publication No. 2002-124154) discloses a key assembly that provides the human operator with tactile feedback in response to human input. The key assembly employs elastically deformable domes that support conductive regions on their undersides. The human operator forces a rigid key down on the top side of the elastically deformable domes to cause the domes to deform so that the underlying conductive regions descend onto electrical contacts of a circuit board to cause current to flow as output. During the transition of the rigid key from its uppermost to its lowermost position, the elastically deformable domes snap to provide a tactile response to the operator as an indication that the electrical output has been produced.
It is desirable that a key assembly provide a single tactile response to an operator's input, but the Iwasaki key assembly referenced above has multiple deformable domes that thereby provide more than a single response. A key assembly with a single elastically deformable dome will provide a single response and also reduce the number of components of the total assembly.
The use of a flexible key instead of a rigid key further reduces the number of components, because a flexible component accompanying a rigid key is no longer needed. FIGS. 1–4 illustrate a key assembly 20 comprising a flexible key 25, and, in a fashion analogous to that of Iwasaki, the flexible key 25 interacts with an elastically deformable support 30 and a circuit board 35 to produce an electrical output.
As shown, for example, in the side view of FIG. 1, the circuit board 35 has a pair of electrical contacts 40 on an exposed section 45 of its upper surface. The top view of FIG. 2 shows that the flexible key 25 is elongated. Such a design is typical for a computer keyboard “shift” key or “space” key. The elongated flexible key 25 has a center portion 50 and first and second side portions 55, 60. The center portion 50 has a center downwardly-extending protrusion 65.
The elastically deformable support 30 has a dome shape, and it supports an electrically conductive region 70 on its underside. The electrically conductive region 70 overlies the pair of electrical contacts 40 of the circuit board 35. The elastically deformable support 30 is positioned under the center portion 50 of the flexible key 25. With reference to FIG. 2, the outer dashed-line circle 75 represents the cross-sectional area of the elastically deformable support 30, and the inner dashed-line circle 80 represents the cross-sectional area of the electrically conductive region 70.
FIG. 1 illustrates the key assembly 20 of prior art under a condition in which the electrically conductive region 70 of the elastically deformable support 30 does not contact the underlying pair of electrical contacts 40 of the circuit board 35. When the key assembly 20 is under this condition, the center position 50 of the flexible key 25 is in a state that will be called the “up position” in the context of the present disclosure.
In contrast, FIG. 3 shows the key assembly 20 under a condition in which the electrically conductive region 70 does contact the underlying pair of electrical contacts 40 of the circuit board 35, and thus an electrical output is produced. When the key assembly 20 is under this condition, the center position 50 of the flexible key 25 is in a state that will be called the “down position” in the context of the present disclosure. (The side portions 55, 60 also have “up” and “down positions,” as discussed below.) The center portion 50 transitions from its up position to its down position when a human operator applies a downward force F of sufficient magnitude on an upper surface 85 of the center portion 50.
The key assembly 20 can include circuitry (not shown) operative to provide a digital output. The digital output of the circuitry indicates whether the center portion 50 of the flexible key 25 has transitioned from its up position to its down position. That is, the circuitry indicates whether the human operator has provided a mechanical input to the key assembly 20.
The key assembly 20 of the prior art cannot provide the electronic output as reliably if the downward force F on the upper surface of the flexible key 25 is not applied to the center portion 50. FIG. 4 illustrates the result of an operator applying a downward force F on an upper surface 90 of the second side portion 60 instead. The second side portion 60, which also has an up position and a down position, moves downward. However, the electrically conductive region 70 of the elastically deformable support 30 does not contact the pair of electrical contacts 40 of the circuit board 35 when the second side portion 60 is in the down position. Therefore, the circuitry does not provide a digital output that is indicative of the human input.
Thus, the burden is on the human operator to exercise care that the application of the downward force F on the flexible key 25 is not too far from the center portion 50. Otherwise, the key assembly 25 will not produce the desired electrical output.